Backlash eliminator for machine tools



i 1942' M. E. 'MARTELLDTT! 2,280,760-

BACKLASH BLIMINATOR FOR MACHINE TOOLS Filed April 25, 1958 4. Sheets sheet l ATTORNEY.

April 1942- M. E. MARTELLOTTI 2,280,7$O

BACKLASH ELIMINATOR FOR MACHINE TOOLS Filed April 25, 1938 4 Sheets-Sheet 2 IQ O f P M. E. MARTELLOTTI 2,280,760

BAGKLASH ELININATOR FOR YMCHINETQOLS I Filed April 25, 1938 4 Sheets-Sheet 3 INVENTOR. /74i/0 5/743/71107/7 Patented Apr. 21, 1942 UNITED STATES PATENT OFFICE 2,280,760 nacnmsn ELIMINATOR ron moms TOOLS Mario E. Martellotti, Cincinnati, Ohio, assignor to The Cincinnati Milling Machine Company, Cincinnati, Ohio, a corporation of Ohio Application April 25, 1938, Serial No. 204,005

28 Claims.

' This invention relates to machine tools, and has for a principal object the provision of improved means for actuating a support thereof in v Other objects and advantages of thepreseiit invention should be readily apparent by reference to the following specification considered in conjunction with the "accompanying drawings illustrative of one embodiment thereof, but it will be understood that any modifications may be made in the specific structural details within the scope of the appended claims without departing from or exceeding the spirit of the invention.

Referring to the drawings in which like reference numerals indicate like or similar parts:

Figure 1 is a front elevation of a machine tool embodying the principles of this invention.

Figure 2 is a detail view partly in section showing the motion transmitting connection between the power transmission and the moving support. Figure 3 is an expanded view of the feed-rapid traverse transmission.

Figure 4 is a detail view of the reversing clutch shifter. v

Figure 5 is a detail view of the shifter for the feed-rapid traverse selector.

Figure 6 is a detail view of the stop plunger and associated connections.

Figure '7 is a diagrammatic view of the hydraulic control circuit with the pilot valve in a position to yield quick'traverse left.

Figure 8 is a diagrammatic view of the hydraulic control circuit with the pilot valve in a position to yield feed left.

Figure 9 is a diagrammatic view of the hydraulic control circuit with the pilot valve in a position to yield quick traverse right.

Figure 10 is a diagrammatic view of the hydraulic control circuit with the pilot valve in a position to yield feed right.

Figure 11 is a diagrammatic view of the hydraulic control circuit showing the connections to the backlash eliminating mechanism.

In Figure l of the drawings there is shown a milling machine as an example of a machine tool to which this invention is particularly adaptable, because in such a machine the tooling operation can produce force components which are capable of causing inadvertent movement of the moving support if any lost motion exists in the actuating mechanism therefor. Since a milling machine constitutes a good example for the application of this invention, it will be explained in connection therewith.

The exemplary milling machine illustrated has a pedestal ill from which uprises a column Ii, in the upper portion of which is rotatably mounted a cutter spindle I! for supporting and rotatinga tool or cutter I3. Any conventional mechanism may be utilized for power rotating the spindle. The front of the column is provided with guide surfaces H upon which a knee II is vertically slidable. The knee in turn has horizontal guideways It for receiving a work table l1 which is movable transversely to the axis of the spindle ii. The table may be provided with suitable means for securing work thereto, such as the T-slot l8 in which T-bolts I! may be mounted for clamping a work piece 20.

A transmission for effecting relative movement between the work support and the tool' support is illustrated in Figure 3 of the drawings. This transmission comprises a constantly driven train including a power actuated shaft 2 l which may be continuously rotated by any suitable source of power such as an electric motor not shown. This shaft is iournaled in the column the bevel gear.

II and connected by bevel gearing 22 to a vertlcal spline shaft 23, the bevel gearing being. fixed with the column and the spline shaft flxed with the knee i5 whereby upon vertical adjustment of the knee, the shaft will slide through The spline shaft drives through a second set of bevel gearing, a horizontal shaft 25 which has a spur gear 28 fixed therewith for rotating the rapid traverse gear 21.

The gear "is keyed to shaft 28 for effecting rotation thereof, and this shaft has a second gear 29 keyed to the endthereof for actuating the feed transmission.

The feed transmission" comprises a gear 30 which is keyed to a shaft SI and driven by the gear 29. The shaft 1| extends the full vwidth of the transmission and drives a change gear 32. The change gear intermeshes with a second change gear 33, and by removing the cover 34 these change gears may be removed and reversed, or other pairs of gears of diflerent ratio substituted therefor, whereby a variety of feed rates is provided for actuation of the work table. The gear 33 issecured to the hub of a gear 35 which is supported for free rotation on the end of shaft 28, and the gear 35 intermeshes with a gear 36 keyed to a sleeve 31 which is supported for free rotation on the shaft 3|. The sleeve 31 has an integral gear 38 which intermeshes with a large pinion 38 of gear couplet 46 which is also supported for free rotation on the shaft 28. The pinion 4| of couplet 48 drives a large gear 42 which is keyed to a sleeve 43 supported for relative rotation with respect to the shaft 3|. The sleeve 43 also has a drive member 44 keyed to the other end thereof. A pair of parallel gear trains terminate in gears 45 and 46 respectively which are supported for free rotation on the sleeve 43. These gears are driven through a pair of cverrunning clutches 41 by gear 42 and actuator 44 respectively.

It will be noted that each of the driving gears in the train between gear 32 and the gear 42 was smaller than the driven gear whereby a desirable rate reduction is effected whereby the gears 45 and 46 are rotated at desired slow rates for effecting feeding movements. The actuators 42 and 44 rotate in the same direction. and rotate the gears 45 and 46 in the same direction through overrunning clutches, these clutches being so ar-' ranged that the gears 46 and 46 can be rotated at afaster rate without interfering with the constant rotation of the actuators.

Rotation at a fast or quick traverse rate is effected by the gear 2'! which is in continuous mesh with a gear 48 supported for free rotation on the sleeve 43. This gear has clutch teeth 49 on one end for interengagement with clutch teeth 56 formed on the face of gear 45; and clutch teeth on the other end for interengagement with clutch teeth 52 on the face of the gear 46. The gear 48 is shifted from one extreme position to the other by a fluid actuated shifter 53 which, as shown in Figure'5, has piston portions 54 and 55 on opposite ends slidabie in cylinders 56 and 51 respectively. The shifter is connected to the gear 48 by means of a shifter fork 58.

It will now be apparent that when the gear 48 is in driving engagement with the gear 451 that the gear 46 will be rotated at a fast rate due to i slippage in the overrunning clutch 41, and the gear 45 will continue to be driven at a slow or feeding rate.

The gear 45 continuously meshes with a gear 59 which is supported for free rotation on a sleeve 66 surrounding shaft 6|. The gear 46 drives a gear 62 through an intermediate idler 63 whereby the gear '62 rotates in a direction opposite to that in which the gear 59 rotates. The opposing faces of gears 59 and 62 are provided with clutch teeth 64 and 65 respectively which are adapted to interengage similar clutch teeth formed on opposing sides of the shiftable clutch member 66. The clutch member 66 is splined at 61 on the sleeve 66. The sleeve 60 is fixed with the shaft 6| for rotation thereof, and this shaft has a gear 68 keyed thereto which intermeshes with gear 69 keyed to a parallel shaft 10. The shaft 76 drives through bevel gears H and 12, as shown in Figure 2, a vertical shaft 13 which extends upward to the under side of the work supporting table ll. At this point the shaft 13 is connected by bevel gearing 14 to a rotatable screw 15, the screw being antiirictionally journalled at opposite ends in the table I! for bodily movement therewith. The bevel gear 14 is held against bodily movement whereby the screw 15 moves axially relative thereto.

It will now be seen that the shaft 6| shown in Figure 3 is the final shaft of the transmission which is adapted to be rotated at feed or rapid traverse rates in accordance with the position of the shiftable members 48 and 66, and that the direction of rotation will depend solely upon the position of the direction determining clutch 66.

This clutch is shifted by a shifter fork 16 secured to the actuator 11, as shown in Figure 4. This actuator has piston portions 18 and 79 formed on opposite-ends and slidably mounted in neutralizing sleeves 80 and 8| respectively. These sleeves are slidably mounted in cylinders 82 and 83 whereby when pressure is admitted to one of these cylinders. such as the cylinder 83, the actuator 19 moves to the limit of its stroke to the left moving the sleeve 66 with it, whereby engagement is effected with gear 59. Similarly, when pressure is admitted to cylinder 82, the shifter is moved to the extreme right moving the sleeve 8| with it and effecting driving engagement of the gear 62. When pressure is admitted to both cylinders at the same time, however, the sleeves 88 and Bi move'toward one another to the limit of their movement, as determined by the shoulders formed thereon, whereby the shifter 16 is moved to a central position and the clutch 66 is out of engagement with gears 59 and 62 whereby the movement of the table stops.

When the reversing clutch 66 is in a neutral position, the table may be'manually moved by means of a manually operable lever 84, which is mounted on the projecting end 85 of shaft 6|.

As shown in Figure 11, the screw 75 has a threaded connection with a nut 86 which is rigidly fixed in a housing 87 attached to the knee l5. It is the relative rotation between the screw 15 and the nut 86 that causes traversing movement of the table I1.

It will be noted from Figure 11 that if the cutter I3 rotates in a clockwise direction, and the table i1 is moved at a feeding rate toward the left, that the teeth of the cutter as they engage the work will create a force component parallel to" the direction of movement of the table, and thereby tend to pull the table in that direction, and if any lost motion exists between the screw l5 and the nut 86, an inadvertent movement of the table will result whereby the table will momentarily move at a rate faster than that dictated by the rate of rotation of the screw creating a possibility of damage to the cutter. It 'is therefore desirable that if the machine is to be used in this manner, that all looseness or backlash between the screw 15 and the'nut 86 be eliminated to prevent this possibility. This invention deals with a simplified mechanism for eliminating this backlash automatically and in a proper direction in accordance with the direction of feed. and so controlled by the rate and direction control mechanism that it is ineffective during the rapid traverse rate.

The backlash eliminating mechanism comprises a piston 88 which surrounds the screw 15, and is operatively connected to the screw by means of threads cut on the interior bore thereof. Means are provided for holding the piston against rotation whereby the screw may move spirally through the nut portion of the piston,

but upon application of fluid pressure to the piston, the nut will bodily move the screw axially. If this axial movement takes place, it will be apparent that the table will be advanced until all lost motion is eliminated between the advancing side of the threads on the screw 15 and the correspondingly engaged surfaces in the nut 85, whereby upon engagement of the cutter with the work, the possibility of inadvertent advancing movement will be eliminated.

The piston 88 is slidably mounted in a cylinder 09 which is formed in the housing 81, and the piston 88 has reduced ends 90 and 9| which simulate piston rods sliding relative to cylinder heads 92 and 93, which serve to close opposite ends of the cylinder. The cylinder head 92 is provided with a series of axially extending lugs 94 which interengage with notches 95 formed in one face of the piston for preventing rotation thereof without interfering with its axial movement.

The opposite ends of cylinder 89 are connected by channels 98 and 91 to a transposition valve 98 having a plunger 99, which in one position will connect channels 95 and 91 to channels I and IN and in the other position will transpose these connections whereby the channel 91 will be connected to the channel I00 and the channel 98 will be connected to the channel IN. The channels I00 and IM terminate in ports I02 and I03 of cylinder blocks I04 and I05. These blocks have diametrical bores I00 and I01 which are adapted to cooperate with annular grooves I08 and I09 formed in the shifter plunger 53 for determining the connection of pressure to the ends of the backlash cylinder. The bores I08 and I01 are connected by channels I08 and I09 to ports H0 and III of a pilot. control valve II2. This valve has a port II3 which is supplied with pressure from a suitable pump I I4 having an intake II5 through which fluid is'withdrawn from a reservoir H8. An emergency relief valve II1 may be connected to the pump delivery channel I I8 for relieving excessively high pressures thereadapted to be manually or automatically operated for controlling the fluid actuation of the rate and direction shifters, and it is to be noted that the opposite ends of the backlash cylinder are connected to the same ports of the pilot valve, that is, the ports I I0 and II I, that the cylinders 82 and 83 are connected to, whereby fluid is supplied to one end or the other ofthe backlash cylinder in accordance with the direction of movement of the table, but should the rate in this direction change to rapid traverse, either the piston portion 54, or the piston portion 55 will be shifted into a position to stop the flow to the backlash cylinder whereby neither end of the cylinder will be supplied with pressure and the V backlash eliminator will be released.

Th channels I08 and I09 have branch connections to ports I20 and HI of a stop valve I22. In the running position of this valve, annular grooves I23 and I24 in plunger I25 interconnect ports I20 and I2I to ports I26 and I21 to which channels are connected leading to cylinders 82 and 83.

When the pilot valve plunger H9 is in the position shown in Figure 11, it connects the source of pressure to channel I09 and thereby to cylinder 83 whereby the direction clutch 88 is shifted to its extreme left position, which causes movement of the table to the left. At the same time pressure is connected to cylinder 08 where- The pilot valve II2 has a plunger II9 which is by the clutch gear 48 is shifted to its right hand position, thus permitting the gear 09 to be rotated at a feed rate. Since the shifter 53 is to the right, the annular groove I09 will connect pressure in channel I09 to the right hand end of the backlash cylinder thereby shifting the piston actuated nut 88 to the left. or'in other will not cause any inadvertent movement of the table.

In Figures 7, 8, 9 and 10 there are diagrammatically shown the different hydraulic connections that the pilot valve can effect for causing feeding movements to the right or left, or quick traverse movement to the right or left with the cutter rotating in a direction to eiTect a hook-in cut, that is, in a direction in which it tends to create a pull on the table in the direction of table movement.

In Figure 7, the parts are shown in a position to cause quick traverse movement to the left. The pilot valve has a sleeve I28 in which is formed an annular pressure groove I29 which is continuously supplied with pressure through port II 3. The sleeve also has annular grooves I30, I3I, I32 and I33 which are permanently connected to ports IIO, III, I34, and I35, the last two ports being connected by channels I35 and I31 to cylinders 58 and 51, as shown in Figure 11. The plunger I I9 is adapted to be moved axially relative to the sleeve into either one of two positions, and is also adapted to be rotated while in either one of these two positions whereby the pilot valve has a total of four different positions.

The plunger has two axial bores I38 and I39 which are closed at both ends, and a series of radial bores intersect these axial bores whereby the pressure from annular groove I29 may enter these axial bores and be selectively distributed in a predetermined manner to the annular grooves I30, I3I, I32 and I33. The plunger also has a second pair of axial bores I40 and I which are opened at one end to form exhaust'or return channels, and radial bores are also provided which intersect these two axial bores for selectively. connecting the annular grooves I30, I3I, I32 and I33 to reservoir.

The pump II4 must be continuously connected to the pressure bores I38 and I39 regardless of the various positions of the pilot valve plunger, and to make this possible, the annular groove I29 is provided with two radial bores I42 and I43 which communicate with a wide annular groove I44 formed in the periphery of the plunger II9 whereby the plunger may be shifted axially without breaking the connection. The annular groove E44 has a pair of radial bores I45 and I48 which intersect the axial bores I39 and 38 respectively. Thus regardless of the position of plunger II9,

the bores I38 and I39 are always under pressure.

In Figure 7, the pressure bore I38 is connected to annular groove I3I by coinciding radial bores I41 and I48 formed in the sleeve and plunger respectively; and to annular groove I33 by a second pair of coinciding radial bores. The axial bore I39 is similarly connected to annular grooves I3I and I33, the purpose being to provide a second connection which is from the first connection so that the valve will be hydraulically balanced. At the same time, the annular grooves I30 and I32 are connected to the exhaust bores I40 and MI by pairs of coinciding radial bores. By means of these connections, the reversing clutch 18 is shifted to the left, and the rapid traverse clutch gear 48 is shifted to the left whereby the table'moves toward the left at a quick traverse rate, and it will be noted that one end of the backlash cylinder is disconnected from pressure by the piston 55, and that the other end is connected to reservoir by the annular groove I08 whereby the backlash mechanism is ineffec tive during this movement.

The pilot valve trip plunger H9 is supported adjacent the front of the table I1, and when the table is moving toward the left, the wing I49 on the plunger is rotated to the right of a central position, as shown in Figure 1. This results in a flat face I50 on the plunger being parallel to the direction of table movement, and on this face is formed a lug I5I. "As the table moves toward the left at a rapid traverse rate, an inclined face I52 on dog I53 engages the under side of the lug I5I and vertically raises the pilot valve plunger H9 into the position in which it is shown in Figures 1 and 2.

This axial movement corresponds to movement of the plunger II9 from the position shown in Figure 7 to the position shown in Figure 8. This results in the pressure bores I38 and I39 being connected by coinciding radial bores to grooves I3I and I32, whereby pressure will still flow in channel I09 thereby maintaining the same direction of movement, but the pressure in channel I32 will cause shifting of the clutch gear 4 8 to its right hand position whereby the gear 59 will now rotate at a feed rate. The shifting of plunger 53 to the right will establish a pressure connection with the backlash eliminator whereby the eliminator will now automatically become effective. The other two annular grooves I30 and I33 will be connected to the reservoir channels I40 and MI.

It will be noted that when the plunger 53 shifted to the right to connect pressure through channel IM to the backlash eliminator, that it also prevented return flow from the other end of the backlash cylinder to the pilot valve. Since the fluid in the left hand end of the backlash cylinder 89 must be exhausted in order to'permit the necessary movement of the piston 88, a bleed- -er coil I54 is connected to a branch I55 of channel I00 whereby the oil will be forced through the 'bleeder coil to a return channel I56.

A second bleeder coil I51 is branch connected to channel IOI so that when pressure is admitted .to channel IOI, fluid can be exhausted from the other end of the backlash cylinder in a similar manner to return line I59.

As the table approaches the end of its feeding stroke to the left, a reversing dog I58 engages: the wing I49 on the pilot valve plunger and rotates the plunger into a rapid traverse right position. This corresponds to the position of the parts shown in Figure 9 in which the pressure bores I38 and I39 are connected through coinciding radial bores to annular grooves I30 and I32, and grooves I3I and I33 are connected to'reservoir. This reverses the conditions existing in channels I08 and I09, the former now being under pressure whereby the reversing clutch 18 will be shifted into its right hand position. Since the rapid traverse gear 48 is already in its right hand position, the-table will move toward the right at a rapid traverse rate, and since the port I08 is closed and the port I01 is'connected to reservoir, the backlash eliminator will be off.

Should it be desirable to change the table rate from rapid traverse to feed, an additional dog I59 may be attached to the table having a downwardly inclined surface I for engaging a lug I81 formed on the plunger H9 and now positioned in projecting relation to the table due to rotation of the plunger by the reversing dog I58. This would put the pilot valve plunger in the position shown in Figure 10, in which the pressure bores I38 and I39 are interconnected by coinciding radial bores to annular grooves I30 and I33 whereby pressure still remains in channel I08, but channel I31 will be connected for pressure shifting the rapid traverse gear 48 to the left whereby the gear 82 may rotate at a feed rate. The shifting of plunger 53 to the left to cause shifting of gear 48 results in the annular groove I08 in plunger 53 connecting the pressure line I08 to the left hand end of the backlash eliminating cylinder whereby the backlash eliminator becomes effective and in the proper direction.

The table may be stopped either manually or automatically by shifting the stop valve plunger I25 to the left, as viewed in Figure 11, whereby pressure will be admitted to both cylinders 82 and 83 in the manner previously described. The plunger I25 is held in the position shown by a latch member I82 which engages a shoulder I83 formed on the end of the plunger, as shown in Figure 6. This latch is withdrawn automatically by providing a dog I54 on the table which will depress the plunger I85 and thereby through the pivoted connection I68 cause rotation of the lever I61 integral with the latch member I82 in a counter-clockwise direction. A spring I88 surrounds the plunger I85 and is interposed between aflxed part I89 of the knee and a collar I10 secured to the plunger. Thus, the spring continuously urges the plunger upward, the movement being limited by a second collar I1I secured to the plunger below the fixed portion I69. When the latch IE2 is withdrawn from engagement with plunger I25, pressure in the chamber I12 at the right hand end of valve casing I22 urges the plunger I25 to the left. This chamber is continuously connected with the pump I44 by a channel I13. The stop valve can only be repositioned in a running position manually by means of a lever I14 secured to the front of the machine, as shown in Figure 1, and attached to the end of a shaft I15, which shaft, as shown in Figure 6, has a ball ended lever I18 engaging a notch I11 formed in the plunger I25. When the lever is rotated in a counterclockwise direction, the plunger I25 moves toward the right, and the movement is continued until the latch I82 drops into position. When the table is to be stopped manually, the lever I14 is rotated in a clockwise direction whereby a lug I18 engages a finger I19 integral with the latch I82 withdrawing the same from engagement with the plunger I25 whereby the hydraulic pressure will again shift the valve to a stop position. In order to permit this movement, the ball ended lever I18 has a lost motion connection with the plunger I25 so that the lever I14 may be rotated a sufiicient distance to effect matically effective during feeding rates and ineffective during quick traverse rates.

What is claimed is:

1. In a milling machine having a cutter support and a work support, the combination of transmission means for effecting relative movement between said supports including a relatively movable screw and nut, one of which is attached to the moving support, a transmission train for effecting relative rotation between said screw and nut including a member shiftable to change the rate of said rotation, at fluid shiftable non-rotatable nut engaging said screw, hydraulic means for shifting saidmember, and means responsive to a feed rate position of said member for coupling hydraulic pressure to effect shifting of the second named nut in the direction of support movement.

2. In a milling machine having a cutter support and a work support, the combination of transmission means for efiecting relative movement between said supports including cooperating threaded elements, one of which is attached to the moving support, a piston actuated nut for eliminating backlash between said threaded elements, said. transmission having a pair of shiftable elements differently positionable for yielding feed and quick traverse rates, a source of fluid pressure, a pilot valve for determining the positioning of said elements by said source of pressure, a valve in series with said pilot valve and one of said shiftable elements for disconnecting said element from the pilot valve, and valve means in the other snii'table element and arranged in series with said piston actuated nut for determining actuation thereof in accordance with the rate or movement of the moving support.

3. In a milling machine having a work support and a cutter support, the combination of transmission means for effecting relative movement between said supports including relatively movable threaded members, one of which is attached to said support, means for effecting relative rotation between said members to effect movement of said support including a direction determining clutch,- a rapid traverse control clutch having difierent positions for a given position of said direction clutch to yield a feed rate or a rapid traverse rate, a piston actuated nut for eliminating backlash between said threaded elements,

channels leading to opposite ends of said piston,

a pilot valve for controlling hydraulic actuation of said rapid traverse clutch and the connection of pressure to said channels, and means operable by said rapid traverse clutch for determining flow in said channels.

4. In a milling machine having a cutter support and a work support, the combination of transmission means for effecting relative movement between said supports, cooperating relatively movable threaded elements for transmitting motion from said transmisssion to the movable support, a piston nut for eliminating lost motion between said threaded elements, said transmission having shiftable feed-rapid traverse rate selecting means, a source of pressure, a pilot valve for variably connecting said source of pressure to said selecting means for determining the rate of movement of said support, channels for supplying fluid pressure to said piston nut, said pilot valve also having means for determining the coupling of fluid pressure to said channel means, and valve means operable by said rate selecting means for determining which end of said piston nut will be connected to said channels.

5. In a milling machine having relatively movable cutter and work supports, the combination of transmission means for effecting relative movement between said supports. said transmission including a fluid operable backlash eliminator and fluid shiftable elements for determining different rates and directions of movement, a source of fluid pressure, a pilot valve for connecting said fluid pressure to determine the position or said elements and thereby the rate and direction of movement of said movable support, channels for supplying fluid pressure to said backlash eliminator, said pilot valve havin means for determining the coupling of fluid pressure to said channels, and valve means controlled by said shiftable elements for determining which one of said channels shall be connected to said eliminator.

6. In a milling machine having relatively movable cutter and work supports, the combination of transmission means for effecting relative ,movement between said supports including a pair of final gear trains, a feed transmission,

a rapid traverse transmission, a shifter for selectively determining actuation of said trains by said transmissions, a backlash eliminator including a piston and cylinder, a pilot valve, 8. source of fluid pressure connected to said pilot valve, means in said shifter for determining which end of said backlash cylinder is connected to the pilot valve, a second shifter for selectively connecting one of said final trains for actuation of the movable support, means in the pilot valve for connecting said cylinder to the source of pressure or to exhaust in accordance as said last named shifter is connected to a feed operated train or a rapid traverse operated train.

7. In a milling machine having a rotatable cutter spindle; a support, a table reciprocably mounted on said support for movement transversely to the axis of said spindle, means for eifectlng movement of said table including a screw rotatably supported by said table, power operable means for rotating said screw, :3. housing mounted on said support, a first nut fixed in said housing and engaging said screw, a second nut mounted in said housing in intermeshing relation with said screw, means to hold said.

second nut against rotation, a piston portion formed on said second nut, a cylinder formed in said housing and containing said piston, and trip controlled means for governing the ad mission of pressure to said cylinder to effect directional shifting of said second nut in accordance with the rate and direction of movement of said support.

8. In a machine tool having a relatively movable tool and work support, the combination of transmission means for eflecting relative movement between said supports including shiitable means for determining different rates of relative movement, a relatively rotatable screw and nut, one of which is carried by themoving support, motion transmitting connections from said transmission to efiect said relative rotation, a piston surrounding said screw and operatively connected thereto for effecting relative axial movement between the screw and nut, a source of fluid pressure, a first control means for potentially connecting a source of pressure to said piston, and additional means controlled by said shiftable means for finally determining if the connection shall be made.

sourceto said piston, and means operable by said shiftable elements for finally controlling the connection of fluid pressure to said piston.

10. In a machine tool having a relatively movable tool and work support, the combination of transmission means for efiecting relative reciprocation between said supports including a screw and nut, one of which is attached to the moving support, a piston surrounding said screw, a threaded connection between said piston and screw, a direction determining clutch, a source of pressure, a-valve for simultaneously connecting said source of pressure to said clutch and to said piston and thus determining the direction of movement between said supports and eliminating backlash between the screw and nut in that direction of movement, an element shiftable to increase the rate of said relative movement, and means operable by said element to interrupt the flow of fluid pressure to said piston during operation at the increased rate.

11. In a machine tool having relatively movable tool and work supports, the combination of transmission means for effecting relative movement between said supports including a relatively rotatable screw and nut, one of which is carried for effecting relative rotation between said threaded members including a reverser, a pair of channels connected to opposite ends of said piston, a source of pressure, means for selectively connecting said source of pressure to one or the other of said channels in accordance with the position of said reverser, a shifter rod operatively connected to a rate change element in said transmission, said shifter rod having portions intercepting said channels for blocking the flow therein and grooves formed in said portions for permitting flow only when said rate change element is in a feed position.

14. In a machine tool having a translatable support and transmission means for effecting said translation including shiftable clutches for changing the rate and direction of said translation, the combination of a piston for removing backlash in the final elements of said transmission, a source of fluid pressure, control means for connecting said pressure to effect fluid shifting of said clutches including a pair of channels connected in parallel to one of said clutches and to said piston whereby said channels may be alternately connected to pressure to control .the direction of movement of said support and means associated witlnthe other clutch for ultimately determining flow in said channels to said piston.

15. A backlash control for the actuating mech- I anism of a machine tool or the like which includes relatively rotatable nut and screw members, said mechanism including a piston member coupled with the screw, a hydraulic power circuit for reaction on said piston member including a source of hydraulic medium, conduits intervening said medium and the piston for vari by the moving support, means for eliminating bleeder connection to the reservoir line.

12. In a machine tool having a work support and a cutter support, the combination of transmission means for effecting relative movement between said supports including a relatively rotatable screw and nut, one of which is attached to the movable support, transmission means for effecting relative rotation between the screw and nut including a plurality of shiftable control elements for determining the rate of relative movement between said supports, hydraulic means for positioning said elements to yield a feed rate, a piston nut for eliminating backlash between the screw and nut, a source of fluid pressure therefor and means in one of said control elements and effective when the element is shifted to a feed position for connecting said fluid pressure to said piston nut to eliminate backlash during the feeding movement.

13. In a machine tool having a pair of relatively movable supports and relatively rotatable threaded members for effecting said movement, the combination of means for removing lost motion between said threaded elements including a piston operatively connected for shifting one of said elements axially of the other, a transmission ably coupling the medium therewith for opposite reactions thereon, a shiftable rate selector, and valve means shiftable with the rate selector and reacting .on the conduits for neutralizing the pressure effect of the hydraulic medium as respects said piston member.

16. A backlash control for the actuating mech anism of a machine tool or the like which includes relatively rotatable nut and screw members, said mechanism including a piston member coupled with the screw, a hydraulic power circuit for reaction on said piston member including a source of hydraulic medium, conduits intervening said medium and the piston for variably coupling the medium therewith for opposite reactions thereon, a shiftable rate selector, valve means shiftable with the rate selector and reacting on the conduits for neutralizing the pressure effect of the hydraulic medium as respects said piston member, a hydraulically actuable reverser for the nut and screw mechanism, conduits coupling the reverser in parallel with the piston for jointly determining the actuations of the reverser and piston, and control valve means for intervening said conduits and the source of hy-- draulic medium for concomitantly reversing the flow to the reverser and piston.

17. A backlash control for the actuating mechanism of a machine tool or the like which includes relatively rotatable nut and screw members, said mechanism including a piston member coupled with the screw, a hydraulic power circuit for reaction on said piston member including a source of hydraulic medium, conduitsintervening said medium and the piston for variably coupling the medium therewith for opposite reactions thereon, a shiftable rate selector, valve means shiitable with the rate selector and reacting on the conduits for neutralizing the pressure effect of the hydraulic medium as respects said piston member, a hydraulically actuable reverser for the nut and screw mechanism, conduits coupling the reverser in parallel with the piston for jointly determining the actuations of the reverser and piston, control valve means for intervening said conduits and the source of hydraulic medium for concomitantly reversing the flow to the reverser and piston, and a transposition valve intervening the piston and reverser devices and shiftable selectively to interchange pressure connections to effect corresponding or opposite movement of the parts for a given position of the control valve means. 18. A control for the drive transmission of a machine tool comprising a translatable member, relatively rotatable nut and screw devices for effecting translation of the member, driving means and rate changing and direction changing devices intervening the driving means and the nut and screw mechanism, said control including a source of hydraulic actuating medium, a piston member coupled with the screw element, coni duits coupled with the source of hydraulic medium and potentially coupleable with said piston and with the rate and direction changing devices of the transmission, a first valve means for determining the directional coupling of the hydraulic medium with the piston and with one of said devices, and additional valve means operatively connected with the other of said devices for neutralizing the effect of the hydraulic medium as respects said piston.

19. A control for the drive transmission of a machine tool comprising a translatable member, relatively rotatable nut and screw devices for effecting translation of the member, driving means and rate changing and direction changing devices intervening the driving means and the nut and screw mechanism, said control including a source of hydraulic actuating medium, a piston member coupled with the screw element, conduits coupled with the source of hydraulic medium and potentially coupleable with said piston and with the rate and direction changing devices of the transmission, a first valve means for determining the directional coupling of the hydraulic medium with the piston and with one of said devices, additional valve means operatively connected with the other of said devices for neutralizin the efiect of the hydraulic medium as respects said piston, and a transposition valve intervening certain of the conduits and the piston for selectively determining the directional tlect of the hydraulic medium on the piston for "a given position of the first-mentioned valve means.

20. In a means for reducing or eliminating backlash between two machine elements the combination of members relatively movable in accordance with backlash between said elements to increase the volume of a restricted space, means for supply of liquid to said space, and means preventing escape of liquid from said space except at a relatively slow rate. 21. A backlash eliminator for machine mechanism including two members relatively movable in accordance with the backlash in said mechanism to increase the volume of a restricted space, a source of pressure liquid, means substantially freely admitting liquid from said source to said space, and restricting means limiting outflow of liquid from said space to a relatively slow rate.

22. The combination of a feed screw, nut

means therefor including two nut portions relatively adjustable for eliminating backlash 0f the nut means relative to said screw, means operative for the relative adjustment of said nut portions' in the direction eliminating backlash, and means subsequently operative to permit reverse direction of movement of the adjusted nut portion and additional means for restricting the rate of said reverse movement thereof.

23. The combination of a. feed screw, nut means therefor including two nut portions relatively adjustable for eliminating backlash of the nut means relative to said screw, means operative for said relative adjustment of the nut portions in the direction eliminating backlash including a piston, a cylinder and a liquid supply source therefor, and means subsequently operative to limit the rate of reverse adjustment of the adjusted nut portion including a restricted outlet for liquid from said cylinder.

24. The combination of a feed screw, nut means therefor including two nut portions relatively axially adjustable, the threads of one of said nut portions contacting the screw threads at the one side thereof to prevent relative movement therebetween in one axial direction, means operative to axially relatively adjust said nut portions until the threads of the other nut portion contact said screw threads at the other side thereof, and means subsequently operative to permit the reverse direction of adjustment of the adjusted nut portion and additional means for restricting the rate of said reverse movement thereof.

25. The combination or a feed screw for relative support movement, nut means for said feed screw including two nut portions relatively axially adjustable, means operative to axially relatively adjust said nut portions until the nut thread elements of the difierent nut portions respectively contact the screw threads on opposite axial sides thereof, means subsequently operative to permit reverse direction of adjustment of the adjusted nut portion and means for automatically controlling the rate of said reverse adjustment.

26. The combination of a feed screw, nut means therefor including two nut portions relatively axially adjustable, the threads of one of said nut portions contacting the screw threads at the one side thereof to prevent relative movement therebetween in one axial direction, means operative to axially relatively adjust said nut portions until the threads or the other nut portion contact said screw threads at the other side thereof, and means subsequently operative to permit the reverse direction of adjustment of the adjusted nut portion including piston and cylinder means having a restricted outlet limiting the rate of said reverse adjustment.

27. The combination of a feed screw, a support, nut means for said screw including a first nut portion, positive abutment means for said support and first nut portion limiting the relative movement therebetween in one direction axially of said screw, said nut means including a second nut portion movable in said direction, whereby to simultaneously eliminate lost motion between said nut means and said screw and between said abutment means, means for movement of said second nut portion in said direction to effect said lost motion elimination, and means subse quently operative to permit opposite movement of said second nut portion including means for restricting the rate of said reverse movement thereof.

28. The combination of a iced screw, a support, nut means for said screw including a first nut portion, positive abutment means for said support and first nut portion limiting therelative movement therebetween in one direction axially of said screw, said nut means including a second nut portion movable in said direction, whereby to simultaneously eliminate lost motion between said nut means and said screw and between said abutment means, means for movement of said second nut portion in said direction to effect said lost motion elimination, and means subsequently operative to permit the oppositemovement of said second nut portion including piston and cylinder means having outlet restricting means limiting the rate of said opposite movements.

MARIO E. L IAR'IELLO'ITI 

